This invention relates to solar collectors and more particular to a solar collector for heating air or other gas.
Solar collectors absorb radiant energy from the sun and deliver heat to a working medium such as air or water. The heated medium is typically used for space heating purposes, and can also provide domestic hot water. A solar collector for heating air typically has an air passage with a glazing layer forming the passage wall that is exposed to the sun. A transfer element is disposed within the passage to absorb solar energy, transform it to heat, and deliver the resultant heat to air in the passage. The transformation converts sunlight, which is radiant energy of relatively short wavelength, to heat, which is radiant energy of longer wavelength.
The transfer element ideally has a large energy-absorbing surface for illumination by the sun, sufficient thermal conductivity for efficient heat delivery, and a large surface for exposure to the flow within the passage of the air that is to be heated. The transfer element in addition is to be low in cost, easy to handle and install in various collector configurations and orientations, and resistant to deterioration with age and under the relatively extreme thermal cycling that occurs between a sunny day and night, as well as between winter and summer. Known transfer elements for hot air solar collectors include finned metal structures, screens, and fibrous structures. Some examples appear in U.S. Pat. Nos. 4,129,117; 4,119,083; 4,095,428; and 3,875,925.
An object of this invention is to provide a solar collector for heating air and which has improved energy transferring efficiency in the sense that it transfers to the air a relatively high percentage of incident solar energy. Further objects are that the collector be relatively low in cost, and provide prolonged use with little if any maintenance.
It is also an object of the invention to provide an energy transfer element for providing a solar collector with the above features, and more particularly which has a large energy-transferring surface relative to the size of the surface. That is, the transfer element is to have such a rough and coarse surface topography that the area of the physical surface is significantly larger than a smooth surface of like peripheral size or dimensions.
Another object of the invention is to provide a solar collector transfer element through which the working medium can flow readily in either direction, which can be mounted in any selected orientation relative to the earth's gravitational field, and which is comparatively light in weight and of low volume.
Yet another object is to provide such a solar collector, and a transfer element therefor, which is of relatively low cost to manufacture and to install and which has a relatively long operating life with low maintenance.
Other objects of the invention will in part be obvious and will in part appear hereinafter.